Spatial Projects SQL (spatialSQL)
for MapInfo Professional®

   Region Smart Centroid and Alignment

The   button, calculates the geometric smart properties of each selected region and directs output to a table. The output can then be joined in a query with the base table and autolabelled. All label output from smart centroid is of autolabel type rather than fixed text objects.

The term smart properties refers to the application of a set of rules specified by the user to determine the best labelling position and alignment of the centroid. It amounts to the best choice of the 3 possible centroids and of horizontal or principal axis aligned orientation. The rules are defined by the user in preferences. The principal axis alignment performs well with a variety of polygon shapes and sizes. It does fail to produce a useful alignment in the obvious case of a near square shape. The smart method handles this case with a specific rule. A full description of the use of these rules is provided in the help file.

also allows an optional frontage position to be calculated. The frontage is taken as the region edge that intersects the principal axis and doesn't intersect another region in the same table. The frontage orientation is the same as the centre orientation or may be set to horizontal. The frontage offset is specified in preferences.  

A symbol object at an angle paTheta to the x axis is located at the geometric centroid. The geosqlid field is the rowid of the source table and is used to link the properties to your data during labelling.

The centroid and angle are sufficient data for input to a labelling application.

Shifted centroid:

Visual centroid:

 

The visual centroid is a preferred label location in most instances. However, even a slight taper on polygon sides can force the centroid to one end of a symmetric shaped region.

 

The area difference rule resolves this by reverting to the geometric centroid in these cases.

 

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Last modified: Mar24, 2008